reflectHoriz and reflectVert can be applied to any sort of
layout (including Mirrored layouts) and will simply flip the
physical layout of the windows vertically or horizontally.

XMonad.Layout.MultiToggle transformers are also provided for
toggling layouts between reflected/non-reflected with a keybinding.
To use this feature, you will also need to import the MultiToggle
module:

import XMonad.Layout.MultiToggle

Next, add one or more toggles to your layout. For example, to allow
separate toggling of both vertical and horizontal reflection: